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| author | Ruslan Bilovol <ruslan.bilovol@gmail.com> | 2021-06-04 01:01:04 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-06-09 12:26:49 +0300 |
| commit | e89bb4288378b85c82212b60dc98ecda6b3d3a70 (patch) | |
| tree | 902329a9974240b3a8fe129d0e890e2dcd680cf1 /Documentation/usb/gadget-testing.rst | |
| parent | 40c73b30546e759bedcec607fedc2d4be954508f (diff) | |
| download | linux-e89bb4288378b85c82212b60dc98ecda6b3d3a70.tar.xz | |
usb: gadget: u_audio: add real feedback implementation
This adds interface between userspace and feedback endpoint to report real
feedback frequency to the Host.
Current implementation adds new userspace interface ALSA mixer control
"Capture Pitch 1000000" (similar to aloop driver's "PCM Rate Shift 100000"
mixer control)
Value in PPM is chosen to have correction value agnostic of the actual HW
rate, which the application is not necessarily dealing with, while still
retaining a good enough precision to allow smooth clock correction on the
playback side, if necessary.
Similar to sound/usb/endpoint.c, a slow down is allowed up to 25%. This
has no impact on the required bandwidth. Speedup correction has an impact
on the bandwidth reserved for the isochronous endpoint. The default
allowed speedup is 500ppm. This seems to be more than enough but, if
necessary, this is configurable through a module parameter. The reserved
bandwidth is rounded up to the next packet size.
Usage of this new control is easy to implement in existing userspace tools
like alsaloop from alsa-utils.
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20210603220104.1216001-4-jbrunet@baylibre.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/usb/gadget-testing.rst')
| -rw-r--r-- | Documentation/usb/gadget-testing.rst | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst index f5a12667bd41..9d6276f82774 100644 --- a/Documentation/usb/gadget-testing.rst +++ b/Documentation/usb/gadget-testing.rst @@ -729,6 +729,7 @@ The uac2 function provides these attributes in its function directory: c_srate capture sampling rate c_ssize capture sample size (bytes) c_sync capture synchronization type (async/adaptive) + fb_max maximum extra bandwidth in async mode p_chmask playback channel mask p_srate playback sampling rate p_ssize playback sample size (bytes) |